Swift PDF

Swift PDF is useful for taking images (from scans, photos, downloads or any other source) and combining them into a single PDF document.

Adobe PDF (Portable Document Format) files are a universal file format that can be viewed on multiple operating systems. Swift PDF was initially designed for creating PDF files of scanned pages to fax, archive and e-mail the documents instead of sending individual pages one at a time. However, it can also be used for photographs, graphics or any other Jpeg, Gif or Bitmap images.
You can set the page sizes to any available paper size (Letter, Legal, A4, etc.), adjust the margins, page orientation and sizing options on each page. There aren't many more options or features than that, but it does its job simply and swiftly, and it's entirely free.